Molten sulfur is produced as a natural raw material and as a by-product in chemical processes, such as the “sweetening” of crude oil. In order to transport the sulfur for eventual disposition, it is commonly maintained in a molten state so that it can be pumped and delivered through pipelines as a viscous liquid. Steam-jacketed tank trucks are commonly utilized to transport the molten sulfur from an industrial production area to a storage location where it is typically pumped from the truck into a sulfur pit or storage tank.
It is important that the sulfur remains molten throughout the truck's tank and pumping system, since any solidification can seriously damage the pump.
The transporting tank trucks are equipped with a covered hatch into which a discharge or loading nozzle from a connecting pipe line is inserted. A shut-off valve is provided for either manual or electronic control of the flow-rate through the pipe line and nozzle into the interior of the tank.
One early method of determining when the molten stream should be shut off was to make a direct visual observation of the rising level of the sulfur in the tank. This method was inherently dangerous, since the molten sulfur has a tendency to splash and could cause severe burns on unprotected flesh. Furthermore, the fumes exiting the hatch as the liquid displaced the gases in the overhead are unpleasant at best, and could contain other vaporized compounds that are hazardous to health if inhaled.
Present methods of determining the temperature and the level of the molten sulfur as it rises in the truck's tank are not satisfactory. The use of instruments such as a capacitance and vibration probes, radar meter probes and ultra-sonic probes have proven to be unsatisfactory. As will be apparent to one of ordinary skill in the art, the result of cooling of the molten sulfur is its solidification on measuring instruments. Although viscous, the molten sulfur has a tendency to splash and the drops formed can rapidly cool to the solidification temperature. The encrusted sulfur has been found to interfere with the accurate performance of various types of liquid measurement instrumentation. The failure to obtain an accurate temperature reading can result in damage to the unloading pumps due to solidified sulfur.
One method for safely controlling the volume of molten sulfur loaded into a tank truck is to provide a scale at the loading station. The truck is weighed as it arrives empty at the loading station and the volumetric capacity of the truck is converted to the equivalent weight of molten sulfur to be loaded. As the weight of the truck approaches the predetermined capacity, the valve can be closed when the desired volume has been added. While this solution is satisfactory, the expenses of installation and subsequent maintenance of one or more scales at the tank truck loading stations is substantial.
It is therefore an object of the present invention to provide an apparatus and method for measuring the level of molten sulfur as the sulfur is discharged into a receptacle, such as a tank truck or storage tank or pit, that is relatively inexpensive and that can be used to reliably provide information on the level of molten sulfur or other similar hot molten materials. Another object of the invention is to provide a durable, damage-resistance measuring and signal-generating device, that can be completely automated for generating a control signal for actuating the molten sulfur flow shut-off valve.